read ether header and only process IPv4 packets

Author: y-code

.gitignore

@@ -31,6 +31,8 @@
 *.out
 *.app
 
+*.swp
+
 # Typical build workspace directory
 build
 

proto/packet.proto

@@ -2,11 +2,12 @@ syntax = "proto3";
 
 package ypcap0;
 
-message Packet {
-  string srcAddress = 1;
-  string dstAddress = 2;
-  int32 srcPort = 3;
-  int32 dstPort = 4;
-  int32 size = 5;
+message IpPacket {
+  bool v6 = 1;
+  string srcAddress = 2;
+  string dstAddress = 3;
+  uint32 srcPort = 4;
+  uint32 dstPort = 5;
+  uint32 size = 6;
 }
 

src/y-pcap-service.cpp

@@ -1,4 +1,5 @@
 #include <boost/beast/core/detail/base64.hpp>
+#include <net/ethernet.h>
 #include <netinet/ip.h>
 #include "packet.pb.h"
 #include "y-pcap-service.h"
@@ -140,11 +141,22 @@ int YPcap0Service::Process(pcap_t *handle, int cnt) const {
 
 void YPcap0Service::HandlePacket(u_char *user, const struct pcap_pkthdr *h, const u_char *bytes) {
     std::cout << "=====================================" << std::endl;
-    std::cout << "Sniffed a packet with length of " << h->len << std::endl;
-    ypcap0::Packet pkt;
-    struct ip *ip_header = (struct ip*)(bytes + 14);
+    std::cout << "Packet Length: " << h->len << std::endl;
+
+    struct ether_header *eth_hdr = (struct ether_header*)bytes;
+    u_short ether_type = ntohs(eth_hdr->ether_type);
+
+    std::cout << "Ether Type: " << ether_type << std::endl;
+
+    if (ether_type != ETHERTYPE_IP)
+        return;
+
+    ypcap0::IpPacket pkt;
+    struct ip *ip_header = (struct ip*)(bytes + sizeof(struct ether_header));
     char* base64 = new char[256];
 
+    std::cout << "IP Version: " << ip_header->ip_v << std::endl;
+
     char src_ip[INET_ADDRSTRLEN], dst_ip[INET_ADDRSTRLEN];
     inet_ntop(AF_INET, &(ip_header->ip_src), src_ip, INET_ADDRSTRLEN);
     inet_ntop(AF_INET, &(ip_header->ip_dst), dst_ip, INET_ADDRSTRLEN);